Detergent compositions in tablet form are described, for example, in GB 911204 (Unilever), U.S. Pat. No. 3,953,350 (Kao), JP 60-015500A (Lion), JP 60-135497A (Lion) and JP 60-135498A (Lion); and are sold commercially in Europe. Tablets have several advantages over powdered products: they do not require measuring and are thus easier to handle and dispense into the washload, and they are more compact, hence facilitating more economical storage.
Detergent tablets are generally made by compressing or compacting a detergent powder, which includes detergent active and detergency builder. EP-A-522766 explains that difficulty has been found in providing tablets which have adequate strength when dry, yet disperse and dissolve quickly when added to wash water. The problem has proved especially difficult with compositions containing insoluble aluminosilicate as detergency builder, but the problem also arises with tablets which contain sodium tripolyphophate as the detergency builder.
This prior document teaches that at least some particles of the composition should be coated with a binder which helps to hold the tablet together and allows a tablet to be made using a lower compaction pressure. The binder can also function as a disintegrant.
U.S. Pat. No. 4,642,197 teaches that the effect of selected tablet disintegration agents in a washing additive tablet may be enhanced by the addition of not more than 7% by weight of an alkali metal salt of short-chain organic mono- or polycarboxylic acid. Sodium acetate and sodium citrate are named.
EP-A-482627 teaches that a detergent composition for compaction into tablets with improved solubility should include potassium carbonate together with nonionic surfactant.
EP-A-711827 teaches that speed of disintegration of tablets can be improved by including a highly water-soluble citrate. Tablet compositions exemplified in that document include sodium citrate dihydrate and also polyethylene glycol as an organic polymeric binder. This document also mentions that sodium acetate can be included in a composition as a lubricant to aid tableting. The trihydrate of sodium acetate is not named. The amount of lubricant is not stated, but it would be appropriate to include only a small amount.
WO 90/02165 mentions a range of materials including sodium acetate trihydrate as tableting aids, preferably used as a small percentage of the composition and preferably of fine particle size. A range of possible functions is attributed indiscriminately to these tableting aids.